If there were adequate notes taken for the scene, a decent guess would be to add light in the form of a gray card exposure. As Francesco has mentioned, the scene brightness range is critical. Can you take a test shot with a step wedge, first, to see what the actual values are for an accurate shutter estimate of underexposure?
With good notes taken of the scene, a known value of underexposure from the shutter and a bit of thought, this may not be too bad. If you can get a reading for the shutter from a step wedge (use the same f stop as the original shot to cut down on variables) you will know exactly how much your underexposure is.
From this test and your notes, you should be able to get an idea of a flash exposure to boost the shadows sufficiently. At that point, it is only a matter of development time for nailing down the top for zone VIII. Please let us know how you fare with the process. Chin up buddy, we've all done things like this. The trick is learning from them. Best wishes for a successful development. tim